Subtracting Integers

Warm Up

1. 8 – 11 = 6. -3 – (-5) =

2. 15 – 21 = 7. -17 – 1 =

3. 0 – (-15) = 8. 1 – (-18) =

4. 15 – 1 = 9. -3 – (-45) =

5. 19 – (-19) = 10. -87 – (-87) =

To subtract an integer, add the opposite of the integer. (Be sure to follow the rules for adding integers!)

When two integers have the same sign, add their absolute values and keep the same sign.

When integers have different signs, subtract their absolute values and use the sign from the integer with the greater absolute value.

Dena owes her aunt $12.00. Her aunt takes away $3.00 of the debt. How much does Dena still owe her aunt?

You have $10.00, but want to buy something that costs $15.00, so you borrow money.

Write and solve an expression to model this situation.

Does a – b = b – a?

Remember, addition is commutative. So a + b = b + a.

For example 3 + 2 = 2 + 3 5 = 5

5 – 3 = 2 and 3 – 5 = (-2)So, subtraction is not commutative.

a – b DOES NOT EQUAL b - a

The temperature at the start of a football game was -1◦F. At halftime, the temperature was -9◦F.

Find the change in temperature.

What happens when we subtract a positive integer from a negative integer?

Is the difference positive or negative?

Remember, subtracting is the same as adding the opposite.

Exit Ticket1. -2 – (-4) = 2. -5 – (-4) =

3. 5 – 7 = 4. -14 – 11 =

5. At 8 A.M. The temperature was -14◦F. By noon, the temperature was 12◦F. Find the difference in temperature. Did it rise or drop?

6. When Iris subtracted -12 – (-12), she got a difference of -24. Is her answer correct? Explain your reasoning.